Up until recently, hydrogels have been based only on hydrophilic components. The need for a new class of hydrogels having both hydrophilic and hydrophobic segments has been highlighted by the increasingly available new therapeutic proteins, peptides and oligonucleotides that are mainly of a hydrophobic nature because it is difficult to homogeneously disperse hydrophobic drugs or hydrophobic bioactive molecules within a totally hydrophilic polymer hydrogel to achieve predictable drug release profiles. Moreover, apart from the need to more effectively handle hydrophobic drugs, hydrogels with hydrophobic and hydrophilic components have the advantages over totally hydrophilic-based hydrogels in maintaining structural integrity for relatively longer periods of time and in mechanical strength.
Despite the need for and advantages of hydrogels having both hydrophilic and hydrophobic components, there are only a few reported studies on these. All these studies rely on either synthesis of copolymers from appropriate monomers without crosslinking or rely on the physical blending of hydrophobic and hydrophilic polymers. The synthesis of copolymer involved copolymerization of polylactide oligomer and polyethylene glycol and did not provide a hydrogel with a crosslinked polymer network or hydrophobic property. The method of physical blending has the major flaw of poor integration between hydrophilic and hydrophobic components, i.e., lack of uniformity throughout the composition.